Field emission cathode device and method for making the same

ABSTRACT

A field emission cathode device includes a substrate, a metal plate attached to the substrate, at least one electron emitter electrical connected with the metal plate, and a filler. The metal plate defines at least one through hole extending through the metal plate. The at least one electron emitter is fixed between the substrate and the metal plate and extends through the at least one through hole. The filler is filled into the at least one through hole to fix the at least one electron emitter.

RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201010604389.2, filed on Dec. 24, 2010 inthe China Intellectual Property Office, the contents of which are herebyincorporated by reference. This application is related to applicationsentitled, “METHOD FOR MAKING FIELD EMISSION CATHODE DEVICE,” filed______ (Atty. Docket No. US30316).

BACKGROUND

1. Technical Field

The present disclosure relates to a field emission cathode device and amethod for making the same.

2. Description of Related Art

Field emission displays (FEDs) are a new, rapidly developing flat paneldisplay technology. Generally, FEDs can be roughly classified into diodeand triode structures. In particular, carbon nanotube-based FEDs haveattracted much attention in recent years.

Field emission cathode devices are important elements in FEDs. A methodfor making field emission cathode device usually includes the steps of:providing an insulating substrate; forming a cathode electrode on thesubstrate; forming a dielectric layer on the cathode electrode; anddepositing a plurality of carbon nanotubes on the exposed cathodeelectrode as the electron emitter. However, the carbon nanotubesfabricated by the CVD method are not secured on the cathode electrode.The carbon nanotubes are prone to be pulled out from the cathodeelectrode by a strong electric field force, thus causing the fieldemission cathode device to have a short lifespan.

What is needed, therefore, is a field emission cathode device that canovercome the above-described shortcomings and a method for making thesame.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referencesto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout several views.

FIG. 1 is a schematic view of one embodiment of a field emission cathodedevice.

FIG. 2 is a schematic, cross-sectional view, along a line II-II of FIG.1.

FIG. 3 is a schematic view of one embodiment of an electron emitter anda metal plate.

FIG. 4 is a schematic view of another embodiment of an electron emitterand a metal plate.

FIG. 5 is a cross-sectional view of one embodiment of a field emissioncathode device having a plurality of electron emitters located in eachthrough hole.

FIG. 6 is a schematic view of one embodiment of a method for making afield emission cathode device.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1 and FIG. 2, a field emission cathode device 10 ofone embodiment includes a substrate 110, a metal plate 130 and aplurality of electron emitters 140. The metal plate 130 is located on asurface of the substrate 110. The metal plate 130 defines a plurality ofthrough holes 132. At least one electron emitter 140 is located in eachof the through holes 132.

The material of the substrate 110 can be insulative material, conductivematerial, or semiconductor material. The insulative material can beglass, ceramic, plastic or polymer materials, to ensure that thesubstrate 110 has a fixed shape and a certain mechanical strength. Theconductive material can be gold, silver, copper, aluminum, or any alloyof the metal mentioned. The semiconductor material can be silicon. Ashape and a thickness of the substrate 110 can be chosen according toactual need. The shape of the substrate 110 can be square or rectangularwith a thickness greater than 15 micrometers.

Referring to FIG. 3, in one embodiment, each through hole 132 has asingle electron emitter 140 located therein. The metal plate 130 has afirst surface 134 and a second surface 136 opposite to the first surface134. The first surface 134 is attached to the substrate 110 by anadhesive layer 120. A material of the adhesive layer 120 can be aheat-resistant adhesive such as epoxy adhesives. The adhesive layer 120can be tightly adhered to both the metal plate 130 and the substrate110.

The material of the metal plate 130 can be gold, silver, copper,aluminum, or any alloy of the metal mentioned. A shape and a thicknessof the metal plate 130 can be chosen according to need. For example, theshape of the metal plate 130 can be square or rectangular with athickness greater than 15 micrometers. In one embodiment, the materialof the metal plate 130 is copper, and the shape of the metal plate issquare with a side length of about 50 millimeters and a thickness ofabout 1 millimeter.

The metal plate 130 has many advantages. For example, the metal is easyto process and form an opening, and has good heat conductivity, thus themetal plate 130 in the field emission cathode device 100 can effectivelyreduce the process cost. The metal plate 130 can also improve the heatdissipation of the electron emitter 140 in application.

The through holes 132 can be arranged in an array or a certain pattern.The cross section of each through hole 132 can be round, rectangular,square, etc. In one embodiment, the cross section of the through hole132 is circular with a diameter in a range from about 3 micrometers toabout 1000 micrometers.

Furthermore, the through hole 132 can be filled with a filler 150. Thematerial of the filler 150 is a thermal conductive material such as tin.The filler 150 is used to fix the electron emitter 140 and improve theheat conductivity between the electron emitter 140 and the metal plate130.

The electron emitter 140 can extend out of the through hole 132.Referring to FIG. 3, the electron emitter 140 does not extend out of thethrough hole 132. The electron emitter 140 includes a first portion 142and a second portion 144. The first portion 142 of the electron emitter140 is fixed between the first surface 134 and the substrate 110. Thelength of the first portion 142 can be selected according to need aslong as at least part of the sidewall of the first portion 142 is incontact with the first surface 134.

The second portion 144 of the emitter 110 is received in the throughhole 132 and extends away from the first surface 134 and the substrate110. The second portion 144 can be substantially perpendicular to thefirst surface 134 and the second surface 136. The second portion 144 canbe used as an electron emission portion.

The filler 150 covers at least part surface of the electron emitter 140,and the electron emission portion is exposed from the filler 150. Theend surface of the electron emission portion and the second surface 136can be at the same plane. The filler 150 can fill part of the throughhole 132 to ensure that the electron emission portion is exposed fromthe filler 150. The electron emitter 140 can be spaced from the sidewall of the through hole 132. The metal plate 130 does not shield theelectron emission and ensures that the electron emission portion canemit electron in the electric field.

Referring to FIG. 4, the electron emitter 140 can further include athird portion 146 located out of the through hole 132 extending abovethe second surface 136. The filler 150 can fill part of the through hole132 or fill the entire through hole 132. In the illustrated embodiment,there is only one electron emitter 140 received in each through hole132. The first portion 142, the second portion 144 and the third portion146 are connected in sequence forming an integrated structure. The thirdportion 146 is now the electron emission portion. In one embodiment, thelength of the first portion 142 is twice the length of the secondportion 144.

Referring to FIG. 5, a plurality of electron emitters 140 can bereceived in each through hole 132. If a plurality of electron emitters140 is received in one through hole 132, the electron emitters 140 canbe spaced from each other or partly in contact with an adjacent electronemitter 140. In one embodiment, two electron emitters 140 are receivedin each through hole 132, and the electron emission portion of eachelectron emitter 140 is spaced from each other to reduce the shieldingeffect.

The electron emitter 140 should be flexible and free standing. Theelectron emitter 140 can be a linear carbon nanotube structure, a carbonfiber, or a silicon nanowire. The electron emitter 140 can be locatedsubstantially parallel or twisted with at least one supporting wire,such as helically around an axial direction of the supporting wire. Adiameter of the supporting wire can range from about 50 micrometers toabout 500 micrometers. The supporting wire can be metal wire such ascopper wire, aluminum wire, silver wire, molybdenum wire, or gold wire.The supporting wire is used to support the electron emitter 140 so thatit has a good free standing property.

In one embodiment, the electron emitter 140 is a linear carbon nanotubestructure. The linear carbon nanotube structure can include at least onecarbon nanotube wire and/or at least one carbon nanotube cable. A carbonnanotube cable includes a plurality of carbon nanotube wires. The carbonnanotube wires in the carbon nanotube cable can be twisted or untwisted.In an untwisted carbon nanotube cable, the carbon nanotube wires aresubstantially parallel with each other. In a twisted carbon nanotubecable, the carbon nanotube wires are twisted with each other. A diameterof the linear carbon nanotube structure can range from about 1micrometer to about 500 micrometers. In one embodiment, the diameter ofthe linear carbon nanotube structure is 50 micrometers.

The untwisted carbon nanotube wire can be obtained by treating a drawncarbon nanotube film drawn from a carbon nanotube array with a volatileorganic solvent. Examples of drawn carbon nanotube film, also known ascarbon nanotube yarn, or nanofiber yarn, ribbon, and sheet are taught byU.S. Pat. No. 7,045,108 to Jiang et al., and WO 2007015710 to Zhang etal. Specifically, the organic solvent is applied to soak the entiresurface of the drawn carbon nanotube film. During the soaking, adjacentparallel carbon nanotubes in the drawn carbon nanotube film will bundletogether, due to the surface tension of the organic solvent as itvolatilizes, and thus, the drawn carbon nanotube film will be pulledtogether to form the untwisted carbon nanotube wire. The untwistedcarbon nanotube wire includes a plurality of carbon nanotubessubstantially oriented along a same direction (i.e., a direction alongthe length of the untwisted carbon nanotube wire). The carbon nanotubesare substantially parallel to the axis of the untwisted carbon nanotubewire. More specifically, the untwisted carbon nanotube wire includes aplurality of successive carbon nanotube segments joined end to end byvan der Waals attractive force therebetween. Each carbon nanotubesegment includes a plurality of carbon nanotubes substantially parallelto each other, and joined by van der Waals attractive forcetherebetween. The carbon nanotube segments can vary in width, thickness,uniformity and shape. Length of the untwisted carbon nanotube wire canbe arbitrarily set as desired. A diameter of the untwisted carbonnanotube wire can range from about 0.5 nanometers to about 100micrometers. Examples of carbon nanotube wire are taught by US PGPub.20070166223A1 to Jiang et al.

The twisted carbon nanotube wire can be formed by twisting the drawncarbon nanotube film using a mechanical force to turn the two ends ofthe drawn carbon nanotube film in opposite directions. The twistedcarbon nanotube wire includes a plurality of carbon nanotubes helicallyoriented around an axial direction of the twisted carbon nanotube wire.More specifically, the twisted carbon nanotube wire includes a pluralityof successive carbon nanotube segments joined end to end by van derWaals attractive force therebetween. Each carbon nanotube segmentincludes a plurality of carbon nanotubes substantially parallel to eachother, and joined by van der Waals attractive force therebetween. Thelength of the carbon nanotube wire can be set as desired. A diameter ofthe twisted carbon nanotube wire can be from about 0.5 nanometers toabout 100 micrometers. Further, the twisted carbon nanotube wire can betreated with a volatile organic solvent after being twisted. After beingsoaked by the organic solvent, the adjacent paralleled carbon nanotubesin the twisted carbon nanotube wire will bundle together. The specificsurface area of the twisted carbon nanotube wire will decrease, whilethe density and strength of the twisted carbon nanotube wire willincrease. The carbon nanotubes in the carbon nanotube wire can besingle-walled, double-walled, or multi-walled carbon nanotubes.

In the field emission cathode device 10, at least part of the electronemitter 140 is fixed between the metal plate 130 and the substrate 110,such that the electron emitter 140 can be firmly fixed in the fieldemission cathode device. Thus, the electron emitter 140 is secured andcannot be pulled out from the metal plate 130 by an electric field forcein a strong electric field. Therefore, the field emission cathode device100 has a long life.

Referring to FIG. 6, one embodiment of a method for making the fieldemission cathode device 100 is provided. The method can include:

(S10) providing the metal plate 130, the substrate 110, the filler 150;

(S20) inserting at least one electron emitter 140 into each through hole132, and attaching a first end portion 142 of the electron emitter 140on the first surface 134;

(S30) attaching the metal plate 130 to the substrate, such that thefirst end portion 142 of the electron emitter 140 is sandwiched betweenthe metal plate 130 and the substrate 110; and

(S40) filling the through hole 132 with the filler 150 to firmly fix theelectron emitter 140 in the through hole 132.

In step (S20), the method of inserting at least one electron emitter 140in each through hole 132 can further include:

(S21) providing a field emission wire supply device supplying acontinuous field emission wire 1401, the field emission wire supplydevice including a hollow needle 202 and a tip 204, wherein the fieldemission wire 1401 extends through the hollow needle 202 and out fromthe tip 204;

(S22) inserting the field emission wire 1401 into one through hole 132,and severing the field emission wire 1401 to obtain at least oneelectron emitter 140;

(S23) repeating the steps (S21) and (S22) until at least one emitter 110is in each through hole 132, if more than one through hole 132.

In step (S21), the inner diameter of the hollow needle 202 can beselected according to the diameter of the field emission wire 1401, andan outer diameter of the hollow needle 202 can be selected according tothe diameter of the through hole 132. The inner diameter of the hollowneedle 202 can be about 5 times to about 10 times the diameter of thefield emission wire 1401, to reduce friction between the field emissionwire 1401 and the hollow needle 202. The field emission wire 1401 canextend out from the tip 204 continuously. The field emission wire supplydevice 200 can further include a robot arm (not shown), a controlcomputer (not shown), and other auxiliary equipment to automateproduction. In one embodiment, the field emission wire 1401 is a linearcarbon nanotube structure cut to form a plurality of electron emitters140.

In step (S22), the method of inserting the field emission wire 1401 intothe through hole 132 includes:

(S221) moving the hollow needle 202, inserting the hollow needle 202into the through hole 132 from the second surface 136 to the firstsurface 134, and supplying the field emission wire 1401 at the sametime;

(S222) fixing the end of the field emission wire 1401 extending out fromthe tip 204 on the first surface 134, such as by a welding or bondingmethod;

(S223) pulling the hollow needle 202 out of the second surface 136through the through hole 132; and

(S224) severing the field emission wire 1401 to obtain the electronemitter 140.

The field emission wire 1401 is then severed to form the electronemitter 140. The field emission wire 1401 can be severed immediatelyafter the field emission wire 1401 is pulled out of the second surface136 so that the severed end of the field emission wire 1401 and thesecond surface 136 are substantially coplanar. Thus, the electronemission portion of the electron emitter 140 and the second surface 136are substantially coplanar. The field emission wire 1401 can also besevered after it is pulled out of the second surface 136 certaindistance to form the electron emitter 140. In this situation, theelectron emission portion extends out of the through hole 132 and abovethe second surface 136. In one embodiment, the length of the electronemitters 140 extending out of the through hole 132 and above the secondsurface 136 are substantially the same.

In step (S224), the field emission wire 1401 can be cut by a method ofmechanical cutting such as a blade, laser scanning, electron beamirradiation, ion beam irradiation, heating by supplying a current,and/or laser-assisted fusing after supplying current.

In step (S30), the method of attaching the metal plate 130 to thesubstrate 110 includes:

(S31) coating a surface of the substrate 110 with a binder, therebyforming a bonding layer 140; and

(S32) attaching the first surface 134 of the metal plate 130 to thesurface of the substrate 110 with the binder.

In step (S31), the binder can be epoxy adhesives.

In step (S32), because the first surface 134 has a part of the electronemitter 140 thereon, the electron emitter 140 is firmly held between themetal plate 130 and the substrate 110.

In step (S40), the filler 150 can be melted and filled into the throughhole 132 with a tool such as a hollow needle. The depth of the filler150 in the through hole 132 can be chosen according to need, so long asthe electron emission portion of the electron emitter 140 can be exposedfrom the filler 150 to emit electrons. In one embodiment, the filler 150is filled entirely in the through hole 132. In the filling process, theelectron emitter 140 should be kept in the centre of the through hole132, to ensure the filler 150 is uniformly distributed around thesidewalls of the electron emitter 140. Therefore, the contact areabetween the electron emitter 140 and the filler 150 can be improved, andaccordingly, the thermal capacity improved. Thus, heat produced by theelectron emitter 140 can be effectively conducted to the surrounding.Further more, the electron emitter 140 can withstand a strong electricfield force.

Furthermore, the method of making the field emission cathode device 100can further include a step of burning the electron emitter 140. Theelectron emission portion of the electron emitter 140 which extends outof the through hole 132 and above the second surface 136 can be burnedusing a flame such as an alcohol lamp. Thus, one part of the electronemitter 140 far away from the metal plate 130 is burned down, butanother part of the electron emitter 140 close to the metal plate 130 isleft due to a high heat conductivity of the electron emitter 140. Alength of the remainder portion of the electron emitter 140 afterburning depends on many factors such as oxidative atmosphere,temperature of flame, diameter of the electron emitter 140, and theconductivity of the metal plate 130. The temperature of the flame can beabout 400° C. to about 900° C. In one embodiment, the oxidativeatmosphere is air, the diameter of the electron emitter 140 is about 50μm, the temperature of the flame is about 450° C., the metal plate 130is a copper plate, and the length of the remainder portion of theelectron emitter 140 is about 0.5 millimeters. After the electronemitter 140 is burned, the stability of the field emission can beimproved. Furthermore, the field emission uniformity can be improved dueto the remainder portion of the electron emitters 140 having the samelength.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

It is to be understood that the above-described embodiments are intendedto illustrate rather than limit the disclosure. Any elements describedin accordance with any embodiments is understood that they can be usedin addition or substituted in other embodiments. Embodiments can also beused together. Variations may be made to the embodiments withoutdeparting from the spirit of the disclosure. The above-describedembodiments illustrate the scope of the disclosure but do not restrictthe scope of the disclosure.

1. A field emission cathode device, comprising: a substrate; a metalplate having a first surface attached to the substrate and a secondsurface opposite to the first surface, the metal plate defining at leastone through hole extending through from the first surface to the secondsurface; at least one electron emitter electrically connected with themetal plate and received in the at least one through hole, the at leastone electron emitter having a first portion and a second portionconnected with the first portion, wherein the first portion is fixedbetween the first surface and the substrate, and the second portion isreceived in the at least one through hole; and a filler filled in the atleast one through hole and fixing the second portion in the at least onethrough hole.
 2. The field emission cathode device of claim 1, whereinthe at least one electron emitter is a linear carbon nanotube structurehaving a plurality of carbon nanotubes substantially parallel to eachother and joined by van der Waals attractive force therebetween.
 3. Thefield emission cathode device of claim 1, wherein an exposed part of thesecond portion of the at least one electron emitter is exposed from thefiller.
 4. The field emission cathode device of claim 3, wherein theexposed part of the second portion of the at least one electron emitterhas the same length.
 5. The field emission cathode device of claim 3,wherein the exposed part of the second portion of the at least oneelectron emitter is spaced from a side wall of the at least one throughhole, an end of the exposed part and the second surface of the metalplate are coplanar and the second portion does not extend beyond thesecond surface, and the second portion is an electron emission portion.6. The field emission cathode device of claim 3, wherein the at leastone electron emitter further comprises a third portion connected withthe second portion, extending out of the at least one through hole, andis an electron emission portion.
 7. The field emission cathode device ofclaim 6, wherein the third portion of the at least one electron emitteris substantially perpendicular to the metal plate.
 8. The field emissioncathode device of claim 1, wherein a plurality of the electron emittersis received in the at least one through hole and spaced from each other.9. The field emission cathode device of claim 1, wherein the fillercovers at least a part of the second portion of the at least oneelectron emitter.
 10. The field emission cathode device of claim 1,wherein the field emission cathode device comprises a plurality ofthrough holes arranged in an array or a certain pattern.
 11. A fieldemission cathode device, comprising: a substrate; a metal platecomprising a first surface attached to the substrate and a secondsurface opposite to the first surface, and defining at least one throughhole extending through from the first surface to the second surface; andat least one electron emitter electrically connected with the metalplate; wherein the at least one electron emitter is received in the atleast one through hole, and a portion of the at least one electronemitter is fixed between the first surface and the substrate.
 12. Amethod for making a field emission cathode device, the methodcomprising: (S10) providing a filler, a substrate, and a metal plate,wherein the metal plate has a first surface and a second surfaceopposite to the first surface, and defines at least one through holeextending through from the first surface to the second surface; (S20)inserting at least one electron emitter into the at least one throughhole; (S30) attaching the first surface of the metal plate to thesubstrate, wherein at least a part of the at least one electron emitteris located between the first surface and the substrate; and (S40)filling each of the at least one through hole with the filler to firmlyfix the at least one electron emitter.
 13. The method of claim 12,wherein the step (S20) comprises: (S21) providing a field emission wiresupply device supplying a continuous field emission wire, the fieldemission wire supply device having a hollow needle and a tip, whereinthe field emission wire extends through the hollow needle and out fromthe tip; (S22) positioning the field emission wire into the at least onethrough hole, and severing the field emission wire to obtain at leastone electron emitter. (S23) repeating the steps (S21) and (S22) if morethan one through hole so that the each of the at least one through holehas at least one electron emitter.
 14. The method of claim 13, whereinthe step (S22) comprises: (S221) inserting the hollow needle into the atleast one through hole and supplying the field emission wire at the sametime; (S222) fixing the end of the field emission wire extending outfrom the tip on the first surface; (S223) pulling the hollow needle outof the second surface through the at least one through hole; and (S224)severing the field emission wire to obtain the at least one electronemitter.
 15. The method of claim 13, wherein the step of severing thefield emission comprises mechanical cutting, laser scanning, electronbeam irradiation, ion beam irradiation, heating by supplying a current,or laser-assisted fusing after supplying current.
 16. The method ofclaim 13, wherein the field emission device comprises a plurality ofelectron emitters, the plurality of electron emitters have the samelength.
 17. The method of claim 12, further comprising a step of burningan end of the at least one electron emitter extending out of the atleast one through hole and above the second surface after the step(S20).
 18. The method of claim 17, wherein the field emission devicecomprises a plurality of electron emitters, a remainder portion of theplurality of electron emitters have approximately the same length. 19.The method of claim 17, wherein a burning temperature is in a range fromabout 450° C. to about 900° C.
 20. The method of claim 17, wherein thestep of burning is performed by using a flame.